ExxonMobil is one of the most valuable corporations on earth (second only to Apple) with a value of about $382 billion.
Who are these men? Sechin has been a confidant of Vladimir Putin since the early 1990s. He had been the defacto leader of the faction of the Russian government populated by former secret agents but left the government in 2010 to become the CEO (and subsequent billionaire oligarch) of the Russian oil company Rosneft. Tillerson has been the CEO of ExxonMobil since 2006 and a part of the company since 1975.
Now, Tillerson is nominated to be the next US Secretary of State.
In 2014 the Russian Federation took over Crimea (which had been part of the Ukraine for many years) as well as part of Eastern Ukraine. The United States then imposed sanctions on The Russian Federation and on some individual people who had been involved. Mr. Sechin was one of those people. Those sanctions prevented ExxonMobil from further cooperation with the oil companies owned by the Russian government. After getting a postponement for a few weeks in order to safely close their arctic facilities that project has been halted.
In the last two weeks, while President-elect Trump has been talking to Tillerson, the value of ExxonMobil has increased by many billions of dollars (from about $357 billion to about $382 billion). As Tillerson owns about 1.8 million shares, a material amount of that increase accrues to his personal benefit.
This is a case where a man of substantial wealth has already had an amazing amount of ability to further increase his own personal wealth through a powerful political position. I have no reason to believe that Tillerson will do anything improper, but I do believe that he could have an apparent conflict of interest.